The present invention relates in general to the packaging and protection of electronic circuits and components, and is particularly directed to a new and improved hermetically sealed electronic circuit package, containing a pressure relief valve. The pressure relief valve is closed during assembly and testing in the atmospheric pressure of an earth borne facility, so as to prevent the entry of foreign matter while equalizing exterior and interior pressure. The valve is subsequently controllably opened in the course of deploying the package into the generally contaminant-free vacuum of a spaceborne environment. This serves to effectively continuously maintain equalization of interior and exterior pressures, and thereby reduce mechanical stresses on the packaging structure, without subjecting the electronics to the potential introduction of contaminants.
High reliability integrated circuits are customarily packaged in hermetically sealed enclosures, in order to protect the packaged circuits and components from potential sources of degradation, such as foreign matter, moisture, corrosives, and the like. The use of such packaging is particularly critical where such circuits of the type intended for spaceborne applications, and therefore can be expected to placed in a very humid ambient that typify launch sites geographically located near the earth""s equator.
Because a spaceborne environment is essentially a contaminant-free vacuum, the structural integrity of the packaging architecture that houses and hermetically seals the circuit must be very robust, since the interior pressure of the package is that (1 Atm.=14.7 lb./sq.in.) of its earth borne assembly, testing and prelaunch facilities, and thus induces stresses in the packaging materials. From a practical standpoint, this means that the hermetically sealing structure is often relatively large and bulky (mechanically complex)xe2x80x94which adds unwanted bulk and weight to the payload, in addition to the entailing the use of a costly assembly process.
In accordance with the present invention, the above-described drawbacks associated with conventional hermetically sealed electronic circuit packaging structures intended for spaceborne applications are effectively obviated by incorporating a controllable pressure relief valve into the package. The pressure relief valve may be a custom made valve, or one selected from a variety of commercially available valves types. Such valves include, but are not limited to a standard xe2x80x98pop-up valvexe2x80x99 of the type that maintains a seal until a given pressure differential is reached and then opens; a mechanical valve, such as a diaphragm; an electromechanical valve, such as a solenoid-actuated microvalve; and an electro-thermal valve of the type that employs a meltable seal that opens in response to the application of a prescribed electrical current.
The incorporation of a pressure relief valve into the hermetically sealed packaging structure serves two purposes. First, it maintains the hermetically sealed integrity of the package during assembly and testing in the (equalized) atmospheric pressure of an earth borne facility, and thereby protects the components from its surrounding (potentially degrading) ambient prior to launch and space deployment. Secondly, upon being controllably opened in the course of placing the package in the generally contaminant-free vacuum of a spaceborne environment, the pressure relief valve enables the package interior to be vented, and thereby equalizes the interior pressure to that of the exterior (xe2x80x98cleanroomxe2x80x99xe2x80x94like) vacuum of the surrounding spaceborne environment. This interior/exterior pressure equalization functionality reduces mechanical stresses on the packaging structure, and thus allows its mechanical complexity to be considerably simplified, thereby reducing weight and cost.